TSOP (The Sound of Philadelphia) was the theme from 'Soul Train,' and was one of the many hits written and produced by Kenny Gamble and Leon Huff for Philadelphia International Records, the label they co-founded. The label is celebrating its 50th anniversary this year. They recorded The O'Jays, Patti LaBelle, Harold Melvin and the Blue Notes, Teddy Pendergrass, Billy Paul, McFadden and Whitehead, Soul Survivors and more. We'll listen back to the interview Terry Gross recorded with Gamble and Huff in 2008, in which they talked about their partnership, their label, and some of their greatest recordings.Also, Kevin Whitehead reviews the album 'Black to Future' by the London quartet Sons of Kemet.